1. Field of the Invention
The present invention relates to a honeycomb structural body and particularly relates to a honeycomb structural body used preferably for a structural body such as a catalyst carrier, an electrochemical cell and so on.
2. Description of Related Art
A honeycomb structural body having a plurality of through holes is used in the fields of automobile, fuel cell and so on. For example, as a catalyst carrier used for purifying an exhaust gas of the automobile, a honeycomb structural body made of cordierite is preferably used from view points of heat resistance, heat shock resistance and purifying efficiency. Moreover, in a field of the fuel cell, a stick-type honeycomb. structural body, in which two kinds of materials i.e. YSZ (yttria stabilized zirconia) and lanthanum chromite are alternately stacked, is invented as a base member for the electrochemical cell from a view point of a high output density.
In any event, during the manufacturing steps of the honeycomb structural bodies used for these purposes mentioned above, a simultaneous extrusion forming method, having the steps of inserting respective materials which construct the honeycomb structural body into respective cylinders and extruding the materials simultaneously to obtain a formed body, is included.
However, when the honeycomb structural body is to be manufactured by means of the extrusion forming method as mentioned above, there are following drawbacks. In the case of the honeycomb structural body made of cordierite used for the catalyst carrier for purifying an exhaust gas of the automobile, a strength at near a center portion of respective walls, which construct through holes, becomes extremely low. In addition, defects are liable to be generated during an extrusion from a die. Therefore, there is a drawback such that a mechanical strength and a spalling resistance of the honeycomb structural body obtained in this manner are deteriorated.
Moreover, in the case of the honeycomb structural body for an electrochemical cell made of the two kinds of materials i.e. YSZ and lanthanum chromite, the thus stacked YSZ and lanthanum chromite are reacted each other. Therefore, there is a drawback such that a mechanical strength is deteriorated since a structure is finely varied.
An object of the invention is to provide a new honeycomb structural body having excellent mechanical strength and spalling resistance.
According to the invention, a honeycomb structural body having a plurality of wall portions and a plurality of cross portions, wherein a plurality of through holes are formed by the wall portions and the cross portions, comprises a structure such that: (1) the cross portions are made of a main material which constitutes the honeycomb structural body; (2) the wall portions have a first wall portion; and (3) a center portion of the first wall portion is made of a sub material which is different from the main material.
FIG. 1 is a cross sectional view showing one embodiment of a honeycomb structural body according to the invention. Moreover, FIG. 2 is a perspective view illustrating an appearance of the honeycomb structural body according to the invention.
In the figures explained below, a portion made of a main material of the honeycomb structural body is shown by a hatched area, and a portion made of a sub material of the honeycomb structural body is shown by a black area. In addition, for making an explanation clearly, dimension ratios and details of respective portions are described differently from the actual honeycomb structural body.
A honeycomb structural body 1 shown in FIG. 1 comprises a plurality of wall portions constructed by first wall portions 2 and second wall portions 3 and a plurality of cross portions 5. Further, the honeycomb structural body 1 comprises a plurality of through holes 4 defined by the first wall portions 2, the second wall portions 3 and the cross portions 5.
The cross portions 5 are formed by the main material constituting the honeycomb structural body 1. Moreover, center portions 2a of the first wall portions 2 are formed by the sub material other than the main material mentioned above, and end portions 2b of the first wall portions 2 are formed by the main material. Further, the entire second wall portion 3 is formed by the main material, and the second wall portions 3 and the cross portions 5 are continued in Q direction of the honeycomb structural body 1.
In this invention, a term xe2x80x9ccross portionxe2x80x9d means a portion formed by intersecting the plurality of wall portions with each other. For example, the cross portions 5 shown in FIG. 1 means a portion formed by intersecting the first wall portion 2 and the second wall portion 3 defining the through hole 4.
Moreover, in this invention, a term xe2x80x9cmain materialxe2x80x9d means a material which constructs mainly the cross portion and a greater part of the honeycomb structural body, and specifically a material which is included in the honeycomb structural body by 50-99 wt %. Further, in this invention, a term xe2x80x9csub materialxe2x80x9d means a different material from the main material, which constructs mainly the center portion of the first wall portion, and specifically a material which is included in the honeycomb structural body by 50-1 wt %.
Therefore, in the case that the honeycomb structural body shown in FIG. 1 is used as the catalyst carrier for purifying the exhaust gas of the automobile, if the center portion 2a of the first wall portion 2 is formed by the sub material such as zirconia, alumina and so on having a larger mechanical strength than that of cordierite used as the main material which constructs the honeycomb structural body 1, it is possible to prevent a strength decrease at the center portion of the wall which is a problem of the known honeycomb structural body. In addition, according to the invention, since it is possible to suppress a defect generation during the extrusion forming from the die, it is possible to easily improve a mechanical strength and a spalling resistance of the honeycomb structural body.
Moreover, the main material is formed by two kinds of materials i.e. YSZ and lanthanum chromite, and two kinds of materials are stacked in such a manner that respective row portions P1 of the through hole 4 shown in FIG. 1 is assumed as one cycle. In this case, the center portion 2a of the first wall portion 2 corresponding to a connection portion between YSZ and lanthanum chromite is formed by the sub material such as lanthanum zirconate and so on which is hardly reacted with YSZ and lanthanum chromite, so that it is possible to prevent a fine variation of the honeycomb structural body.
Further, as shown in FIG. 1, the sub material is used only at the center portion 2a of the first wall portion 2 which is a part of the honeycomb structural body. Therefore, it is possible to improve the defects which are existent in the known honeycomb structural body without affecting properties of the known catalyst carrier for the automobile or the known electrochemical cell.